Radiation shield having a plurality of strings rotatable between an open and closed position



Oct. 18, 1966 c. c. ABT ETAL 3,280,331

RADIATION SHIELD HAVING A PLURALITY OF STRINGS ROTATABLE BETWEEN AN OPENAND CLOSED POSITION Filed Nov. l5, 1963 INVENTORS Czlel 6.1987' UnitedStates Patent 3,280,331 RADIATION SHIELD HAVING A PLURALITY OF STRINGSROTATABLE BETWEEN AN OPEN AND CLOSED POSITION Clark C. Abt and George F.Vanderschmidt, Cambridge,

Mass., assignors to the United States oi America as represented by theSecretary of the Air Force Filed Nov. 15, 1963, Ser. No. 324,141 3Claims. (Cl. Z50-108) This invention relates to a radiation shield foruse in areas of radiation of different energy levels.

One object of the invention is to provide, with a given amount of massshielding, protection which may be used selectively for both high energyand low energy radiation.

Another object of the invention is to provide a radiation protectiveshield, from a given rnass of radiation shielding material, which willreduce the density of high energy radiation in one selected position andwhich will absorb substantially all of the low energy radiation inanother selected position of theI shield.

These and other objects will 'be more fully understood from thefollowing detailed description taken with the drawing, wherein:

FIG. l shows a conventional radiation shield for use in a field of highenergy radiation;

FIG. 2 shows a conventional radiation shield with less mass than thedevice of FIG. l in a field of high energy radiation;

FIG. 3 is a schematic showing of a radiation shield according to theinvention in its high energy shielding open position;

FIG. 4 shows the device of FIG. 3 in its low energy shielding closedposition;

FIG. 5 shows a modification of the device of FIG. 3 in its high energyshielding position; and,

FIG. 6 shows the device of FIG. 5 in its low energy shielding closedposition.

It is a well-known principle of nuclear physics that energetic particlessuch as electrons, protons, and neutrons penetrate a given type of massshield to a depth proportional to their energies. If a threateningshower of, say, solar protons has an energy of up to 30 billion electronvolts (b.e.v.), then mass shielding sufficient to stop 30 b.e.v.energies, as shown in FIG. 1, will stop all of the particles, and massshielding not suciently thick to stop 30 b.e.v. particles, as shown inFIG. 2, will let all the 30 b.e.v. particles through with reducedenergy. This is sometimes called the principle of range of penetrationof 'high energy particles. Now, if there is a fixed area to be protectedagainst radiation shielding, and only a given quantity of shieldingmaterial available, it has heretofore ybeen assumed that the optimumdistribution of this material is in a uniform layer over the area to beprotected. This is not necessarily the case and, as a matter of fact, inthose cases where the thickness of a uniform layer of material availablefor shielding is less than the range of penetration of the expectedradiation, the shielding will not only be ineffective but may actuallyincrease the hazards to human Ibeings relying on it by reducing theenergy of the penetrating radiation to a lower level at which it mayhave enhanced biological effectiveness.

According to this invention, slats or strips of shielding material areuniformly spaced over the area to be shielded.

While it is true that radiation enters through the space between theslats, the slats can now be perhaps some two times as thick as theoriginal uniformly distributed shielding material and, if the originaluniformly distributed material was just over half as thick as it neededto be to stop the radiation of a given energy, then if half the area iscovered with strips twice the thickness of the original uniform area,the effective flux will be cut in half. The energy of the radiation thatpasses through the gaps between the slat shield will of course beundiminished, but p the flux density will *be cut in half and,therefore, the biological effectiveness of the radiation will becorrespondingly reduced. In the conventional application, where the sameweight of shielding was applied uniformly, the flux was not diminishedat all since the' energy of the particles was suiicent for all of themto pass through the shielding, the only eect being the reduction of theenergy of the radiation passing through the shielding. The reduction ofthis particle e'nergy could enhance its lethality to biologicalorganisms at worst and, at best, would leave its lethality relativelyundiminished.

Since a man might be killed if he were to remain stationary behind sucha shield, it is necessary that the halfarea protected by the strips bemixed somehow with the half-area that is unprotected. This can usuallybe achieved by the movement of the man behind the shield but, if this isnot possible, movement of the shield may be required. In many cases,however, the shield will be used with vehicles that are moving withrespect to the radiation source so that no additional movement of theshield is required. In space applications the shield may be rotatedaround the space craft or, in some cases, the space craft itself may berotated so that the radiation will not be concentrated in certain stripareas of the body.

Referring now to FIG. 3 of the drawing which shows a Slat shieldingdevice according to the invention, a plurality of slats 10 of shieldingmaterial are spaced apart by a distance equal to less than half of theirthickness T. Each of the slats 10 is geared to a rack shownschematically at 11 by means of gears 12. A shield operating mechanism13 is provided to selectively rotate the slats from the opened positionshown in FIG. 3 to their closed position as shown in FIG. 4. It isobvious that other means may be provided for rotating the slats. In theposition shown in FIG. 3, which is for use in high energy radiation, theslats are in their open position so that they will reduce the fluxdensity of the radiation passing the shield.

If the device using the shielding is moved to a low energy radiationenvironment, the slats may -be rotated to the position shown in FIG. 4.The spacing of the slats should be such as to provide sutiicient overlapto provide protection for the low energy radiation t0 be encountered.

Instead of overlapping sections, abutting sections may be provided asshown in FIGS. 5 and 6. In this arrangement, the slats 20 have matchingcurved ends to permit rotation between their closed abutting positionand their opened position. rlhe operating means may be the same as inFIGS. 3 and 4.

There is thus provided a radiation shield which will providesubstantially complete protection from low energy radiation in oneposition and which can be rotated to a second position to providepartial protection from high energy radiation without a change in thetotal mass.

While certain specific embodiments have been described, it is obviousthat numerous changes may be made without departing from the generalprinciple and scope of the invention.

We claim: 1

1. A device for shielding against energetic particles such as electrons,protons and neutrons comprising, a plurality of slats of shieldingmaterial, having a thickness approximately equal to twice their width,rotatably mounted and spaced from each other by a distance not greaterthan half their thickness and approximately equal to their width, andmeans for rotating said slats between an open and closed position toprovide a reduction in the flux density of high energy radiation in theopen position of said slats and to provide substantially completeabsorption of low energy radiation in the closed position of said slats.

2. A device' for shielding against energetic particles such aselectrons, protons and neutrons comprising, a plurality of slats ofshielding material, having a thickness approximately equal to twicetheir width, rotatably mounted and spaced from each other by a distancenot greater than half their thickness and approximately equal to theirwidth, and means for rotating said slats between an open positionwherein the slats are spaced apart in substantially parallel relation toeach other to provide a reduction in the flux density of high energyradiation and to a closed position wherein there is no space between the4slats to provide substantially complete absorption of 10W energyradiation.

3. The method for obtaining optimum radiation shielding effectivenesswith a fixed mass of shielding material comprising, spacing a pluralityof elongated slats of radia tion shielding material, having a thicknessapproximately equal to twice their width, apart by a distance of notgreater than one-half the thickness of the slats and with the spacesbetween the slats approximately equal to the Width of the slats,providing rotation for said slats about their longitudinal axis tothereby permit reduction of the ux density of high energy radiation inone position of said slats and substantially complete absorption of lowenergy radiation in another position of said slats.

References Cited by the Examiner FOREIGN PATENTS 635,489 3/1928 France,

RALPH G. NLSON, Primary Examiner.

S. ELBAUM, Assistant Examiner.

1. A DEVICE FOR SHIELDING AGAINST ENERGETIC PARTICLES SUCH AS ELECTRONS,PROTONS AND NEUTRONS COMPRISING, A PLURALITY OF SLATS OF SHIELDINGMATERIAL, HAVING A THICKNESS APPROXIMATELY EQUAL TO TWICE THEIR WIDTH,ROTATABLY MOUNTED AND SPACED FROM EACH OTHER BY A DISTANCE NOT GREATERTHAN HALF THEIR THICKNESS AND APPROXIMATELY EQUAL TO THEIR WIDTH, ANDMEANS FOR ROTATING SAID SLATS BETWEEN AN OPEN AND CLOSED POSITION TOPROVIDE A REDUCTION IN THE FLUX DENSITY OF HIGH ENERGY RADIATION IN THEOPEN POSITION OF SAID SLATS AND TO PROVIDE SUBSTANTIALLY COMPLETEABSORPTION OF LOW ENERGY RADIATION IN THE CLOSED POSITION OF SAID SLATS.